There is a continuous effort to develop imagers and detectors for nuclear, biological and chemical (NBC) warfare defenses. The objective is to develop an integrated system of nuclear, chemical and biological sensors in real time during day or night from a remote vantage point. Such a system would provide the capability to detect and survive an initial NBC attack.
A typical ultraviolet (UV) optical system includes optical components for focusing photons produced during the decay of β- and γ-radiations onto a UV filter sensor, a filter for reducing the amount of radiation not in the UV window (e.g., 200-350 nm), and electronics which process and act on signals from the UV sensitive sensor. To date, most UV optical filters include a series of optical filter elements that are stacked to achieve a desired spectral response. Each optical filter element in the series is a single separate optical filter.
There are a variety of devices which use ultraviolet (UV) light filters that allow selected wavelengths of light to pass through. For example, such filters are used in passive missile approach warning systems (PMAWS) which locate and track sources of ultra-violet energy, enabling the system to distinguish the plume of an incoming missile from other UV sources that pose no threat.
All UV sensors have finite sensitivity to visible radiations. It is very important for a UV sensor to discriminate against the visible radiation so as to maximize UV sensitivity while minimizing false signals caused by visible light sources. Therefore, the UV filters should have high transmittance in the UV spectral region and have strong absorption at longer wavelengths. Moreover, the filters should have high thermal stability because the nuclear sensors may be used in environments with high temperatures, such as aircrafts parked in tropical and desert areas.
It is known that certain transition metal ions, such as Ni2+ and Co2+, absorb visible radiations and transit in certain UV range. These metals have been used in UV filters such as Corning 9863 glass which is a UV transmitting glass doped with Ni2+ and Co2+. The doped glass provide effective blocking of visible radiations. However, there is a significant absorption in 250-300 nm wavelength region that sacrifices in-band transmittance and reduces the sensitivity of the detector.
Radiation emitted from a nuclear fission is typically detected by directly detecting the presence of high energy β- and γ-particles. The detection method, however, requires a sensor being placed in the close vicinity of the radiation source because β-particles lost their energy over a range from centimeters to meters and γ-particles lost their energy over a range in the order of hundreds of meters in air.
Therefore, there still exists a need for nuclear detectors capable of detecting nuclear radiation over an extended distance.